A and B together can complete a piece of work in 15 days and B alone can complete it in 21 days. In how many days can A complete it alone?
Show answer & explanation
Correct answer: B
Explanation
The correct answer is option 2 i.e. days.
Let the total work to be completed (LCM of 15 and 21) be 105 units.
Efficiency of A and B = 105/15 = 7 units/day
Efficiency of B alone = 105/21 = 5 units/day
Now, efficiency of A alone = 7 - 5 = 2 units/day
Time taken by A alone to complete the work = 105/2
⇒ days